Radiation-curable ink composition, ink jet recording method, and recorded matter

ABSTRACT

Provided are a radiation-curable ink composition including phenoxyethyl acrylate (A) in an amount of from 20 to 55 mass % of the total reaction components, a multifunctional acrylate (B) in an amount of from 20 to 50 mass % of the total reaction components, and a black pigment (F1); and a radiation-curable ink composition including phenoxyethyl acrylate (A) in an amount of from 20 to 55 mass % of the total reaction components, a multifunctional acrylate (B) in an amount of from 10 to 50 mass % of the total reaction components, and a yellow pigment (F2).

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.14/228,885 filed Mar. 28, 2014, which is a continuation application ofU.S. application Ser. No. 13/903,325 filed on May 28, 2013, now U.S.Pat. No. 8,709,549, issued Apr. 29, 2014, which is a continuationapplication of U.S. application Ser. No. 12/979,912 filed on Dec. 28,2010, now U.S. Pat. No. 8,470,904, issued Jun. 25, 2013. Thisapplication claims the benefit of Japanese Patent Application No.2009-297010 filed Dec. 28, 2009. The disclosures of the aboveapplications are incorporated herein by reference in their entireties.

BACKGROUND

1. Technical Field

The present invention relates to a radiation-curable ink composition andrelates to an ink jet recording method and recorded matter using the inkcomposition.

2. Related Art

Recently, radiation-curable inks, which are cured by ultraviolet,electron beams, or other radiation, have been being developed. Suchradiation-curable inks can dry rapidly and achieve recording preventedfrom bleeding of the inks in recording on non-absorbent media that donot or hardly absorb inks, such as plastic, glass, and coated paper.Such radiation-curable inks are composed of, for example, polymerizablemonomers, polymerization initiators, pigments, and other additives.

Incidentally, a recorded matter where an image is recorded on arecording medium having flexibility, such as a polyethyleneterephthalate resin or a vinyl chloride resin, may be stuck on anarticle having a curved surface, such as an automobile body. Since, insuch purposes, the recorded matter is usually stretched and stuck on anarticle, it is desirable that the image recorded on the recording mediumhave a degree of stretch of 100% or more so that cracking and peeling donot occur even if the image is stretched and be provided with durabilityat the degree of stretch.

In known radiation-curable inks, in order to record flexible imageshaving a degree of stretch of 100% or more, polymerizable monomers, suchas a long-chain alkyl acrylate, a phenoxyethyl acrylate, an ethyleneoxide adduct of a phenoxyethyl acrylate, or an acrylated amine compound,have been used (for example, see JP-A-2006-199924, JP-A-2007-131754,JP-A-2008-7687, and JP-A-2009-35650).

However, in black inks and yellow inks (in particular, black inks) amongthe above-mentioned radiation-curable inks that can record flexibleimages having degrees of stretch of 100% or more, agglomeration spots(gloss unevenness) have occurred on the surfaces of some recordedimages. Such a phenomenon does not occur in cyan inks and magenta inksand is specific to black inks and yellow inks.

Furthermore, even in images recorded using radiation-curable inkscontaining specific polymerizable monomers as described above, crackingoccurs within several hours if the images are maintained in the statethat the recording media are also stretched (for example, at a degree ofstretch of 100%), and problems such that the images are peeled off fromthe recording media are further caused.

SUMMARY

An advantage of some aspects of the invention is to provide black andyellow radiation-curable ink compositions that can impart excellentflexibility to recorded images and inhibit occurrence of agglomerationspots (gloss unevenness) on the surfaces of the images.

The invention can be achieved as the following aspects or applicationexamples.

APPLICATION EXAMPLE 1

A radiation-curable ink composition according to an aspect of theinvention includes:

phenoxyethyl acrylate (A) in an amount of from 20 to 55 mass % of thetotal reaction components;

a multifunctional acrylate (B) in an amount of from 20 to 50 mass % ofthe total reaction components; and

a black pigment (F1).

APPLICATION EXAMPLE 2

A radiation-curable ink composition according to an aspect of theinvention includes:

phenoxyethyl acrylate (A) in an amount of from 20 to 55 mass % of thetotal reaction components;

a multifunctional acrylate (B) in an amount of from 10 to 50 mass % ofthe total reaction components; and

a yellow pigment (F2).

The radiation-curable ink composition according to the applicationexample 1 or 2 is excellent in flexibility in recorded images and caninhibit occurrence of agglomeration spots (gloss unevenness) on thesurfaces of the images, by combining the components as described above.

APPLICATION EXAMPLE 3

In the application example 1 or 2, the multifunctional acrylate (B) maybe at least one selected from dipropylene glycol diacrylate,tripropylene glycol diacrylate, tetraethylene glycol diacrylate,tricyclodecane dimethanol diacrylate, and propoxylated neopentyl glycoldiacrylate.

APPLICATION EXAMPLE 4

In any one of the application examples 1 to 3, the ink composition canfurther contain N-vinyl caprolactam (C) as a reaction component.

APPLICATION EXAMPLE 5

In any one of the application examples 1 to 4, the ink composition canfurther contain an aminoacrylate (D) as a reaction component.

APPLICATION EXAMPLE 6

In any one of the application examples 1 to 5, the ink composition canfurther contain a monofunctional acrylate (E) having an alicyclicstructure as a reaction component.

APPLICATION EXAMPLE 7

In the application example 6, the monofunctional acrylate (E) having analicyclic structure may be at least one selected from dicyclopentenylacrylate, dicyclopentanyl acrylate, and dicyclopentenyloxyethylacrylate.

APPLICATION EXAMPLE 8

In any one of the application examples 1 to 7, the ink composition canhave a viscosity of from 10 to 40 mPa·s at 20° C. and a surface tensionof from 20 to 30 mN/m at 20° C.

APPLICATION EXAMPLE 9

An ink jet recording method according to an aspect of the inventionincludes the steps of:

(a) discharging a radiation-curable ink composition according to any oneof the application examples 1 to 8 onto a recording medium; and

(b) irradiating the discharged radiation-curable ink composition withactive radiation having a peak emission wavelength ranging from 350 to400 nm using an active radiation source.

APPLICATION EXAMPLE 10

A recorded matter according to an aspect of the invention is thatrecorded by the ink jet recording method according to the applicationexample 9.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, where like numbers reference like elements.

FIG. 1 is a perspective view of an ink jet recording apparatus capableof being applied to an ink jet recording method according to anembodiment.

FIG. 2 is a front view of the active radiation-irradiating device shownin FIG. 1.

FIG. 3 is a fragmentary view taken in the direction of the arrowsIII-III of FIG. 2.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Preferred embodiments of the invention will be described below. Theembodiments described below merely describe examples of the invention.The invention is not limited to the following embodiments and caninclude various modifications performed within the scope of theinvention. Note that the term “image” in the invention refers to aprinted pattern formed of dots and includes text printing and solidprinting.

1. RADIATION-CURABLE INK COMPOSITION

The radiation-curable ink composition according to the inventionincludes the following two aspects.

A radiation-curable (black) ink composition according to an embodimentof the invention includes phenoxyethyl acrylate (A) in an amount of from20 to 55 mass % of the total reaction components, a multifunctionalacrylate (B) in an amount of from 20 to 50 mass % or the total reactioncomponents, and a black pigment (F1).

A radiation-curable (yellow) ink composition according to an embodimentof the invention includes phenoxyethyl acrylate (A) in an amount of from20 to 55 mass % of the total reaction components, a multifunctionalacrylate (B) in an amount of from 10 to 50 mass % of the total reactioncomponents, and a yellow pigment (F2).

Each component used in the respective embodiments will be described indetail below.

1.1. Reaction Component

The term “reaction components” in the invention refers to polymerizablemonomers used for forming polymers and does not refer to additives otherthan then the polymerizable monomers, such as pigments, dispersants,photopolymerization initiators, and slip agents. The reaction componentsused in the embodiments will be described in detail below.

1.1.1. Phenoxyethyl Acrylate (A)

The radiation-curable ink composition according to an embodimentincludes phenoxyethyl acrylate (A) in an amount of from 20 to 55 mass %of the total reaction components. The radiation-curable ink compositionaccording to the embodiment can improve flexibility of an image recordedon a recording medium by containing a predetermined amount of component(A) therein.

Component (A) also functions as a solvent for dissolving aphotopolymerization initiator described below. In addition, component(A) shows good reducibility for other acrylate monomers and does notinhibit functions of other acrylate monomers.

When the total mass of the reaction components is assumed to be 100 mass%, the content of component (A) is from 20 to 55 mass %, preferably from25 to 55 mass %, and more preferably from 40 to 55%. By controlling thecontent of component (A) in the total reaction components to theabove-mentioned range, an image recorded on a recording medium can beflexible and have a large degree of stretch, and cracking and peeling donot occur in the image even if the image is maintained in the state thatthe recording medium is also stretched. If the content of component (A)is lower than 20 mass % of the total reaction components, the degree ofstretch of an image recorded on a recording medium becomes small,causing cracking and peeling in the image and significantly reducing thestretching resistance of the image. Furthermore, a photopolymerizationinitiator described below may not be completely dissolved in the inkcomposition. On the other hand, if the content of component (A) ishigher than 55 mass %, the curing property of an image recorded on arecording medium may be deteriorated. In addition, since the content ofcomponent (B) is relatively reduced, agglomeration spots (glossunevenness) may occur on the surface of an image recorded on a recordingmedium.

1.1.2. Multifunctional Acrylate (B)

When a black pigment is used, the radiation-curable ink compositionaccording to the embodiment includes a multifunctional acrylate (B) inan amount of from 20 to 50 mass % of the total reaction components. Whena yellow pigment is used, the ink composition includes themultifunctional acrylate (B) in an amount of from 10 to 50 mass % of thetotal reaction components. The radiation-curable ink compositionaccording to the embodiment can inhibit occurrence of agglomerationspots (gloss unevenness) on the surface of an image recorded on arecording medium by containing a predetermined amount of component (B)therein.

The mechanism of generating agglomeration spots (gloss unevenness) onthe surface of an image recorded on a recording medium can be understoodas follows: Black pigments and yellow pigments have high tendencies ofabsorbing part of active radiation (particularly in the ultravioletregion) compared to other pigments such as cyan pigments and magentapigments. Therefore, in the black inks and the yellow inks, since theenergy of irradiated active radiation becomes insufficient forcompletely curing a film discharged on a recording medium, curing mayoccur only near the surface of the film and be incomplete in the insideof the film or may take a long period of time. It is thought that theuncured ink composition present in the inside of the film, for example,randomly flows before curing to cause agglomeration spots (glossunevenness). The tendency of causing agglomeration spots (glossunevenness) is significant, in particular, in black inks containingblack pigments.

Multifunctional acrylate (B) has a function as a cross-linking agent forenhancing the reactivity of a film discharged on a recording medium and,therefore, can increase the reactivity of a black ink or a yellow inkagainst the film. It is thought that this can inhibit occurrence ofagglomeration spots (gloss unevenness) on the surface of an imagerecorded on a recording medium by the radiation-curable ink compositionaccording to the embodiment.

Examples of multifunctional acrylate (B) include bifunctional acrylates,trifunctional acrylates, and tetrafunctional acrylates.

Examples of the bifunctional acrylate include 1,4-butanediol diacrylate,1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, 1,10-decanedioldiacrylate, 2-hydroxy-3-acryloyloxypropyl methacrylate, ethylene glycoldiacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate,tetraethylene glycol diacrylate, polyethylene glycol diacrylate,dipropylene glycol diacrylate, tripropylene glycol diacrylate,triisopropylene glycol diacrylate, 1,3-butylene glycol diacrylate,poly(butanediol)diacrylate, tricyclodecane dimethanol diacrylate,ethoxylated bisphenol A diacrylate, propoxylated neopentyl glycoldiacrylate, and propoxylated bisphenol A diacrylate.

Examples of the trifunctional acrylate include trimethylolpropanetriacrylate, pentaerythrithol triacrylate, ethoxylated isocyanuratetriacrylate, and ε-caprolacton-modifiedtris-(2-acryloxyethyl)isocyanurate.

Examples of the tetrafunctional acrylate include pentaerythritoltetraacrylate, ethoxylated pentaerythritol tetraacrylate, andditrimethylolpropane tetraacrylate.

The above-mentioned bifunctional, trifunctional, and tetrafunctionalacrylates may be used alone or in combination of two or more.

Among the above-mentioned multifunctional acrylates, the bifunctionalacrylates are preferred from the viewpoint of flexibility of imagesrecorded on recording media, and dipropylene glycol diacrylate,tripropylene glycol diacrylate, tetraethylene glycol diacrylate,tricyclodecane dimethanol diacrylate, and propoxylated neopentyl glycoldiacrylate are more preferred.

When the total mass of the reaction components is assumed to be 100 mass%, the content of multifunctional acrylate (B) in a black ink containinga black pigment is from 20 to 50 mass % and preferably from 30 to 50mass %. As described above, since the tendency of causing agglomerationspots (gloss unevenness) is significant, in particular, in black inks,it is necessary to control the content of component (B) in the black inkto 20 mass % or more. If the content of multifunctional acrylate (B) islower than 20 mass % of the total reaction components, agglomerationspots (gloss unevenness) may occur on the surface of an image recordedon a recording medium. In addition, there is a tendency that scratchresistance of an image recorded on a recording medium is deteriorated.On the other hand, if the content of multifunctional acrylate (B) ishigher than 50 mass %, an image recorded on a recording medium tends todecrease its flexibility, and agglomeration spots (gloss unevenness)tend to easily occur in the image recorded on the recording medium. Inaddition, since the viscosity of the radiation-curable ink compositionis increased, clogging of nozzles of ink jet printers tends to easilyoccur.

When the total mass of the reaction components is assumed to be 100 mass%, the content of multifunctional acrylate (B) in a yellow inkcontaining a yellow pigment is from 10 to 50 mass % and preferably from20 to 50 mass %. As described above, it has been confirmed that thetendency of causing agglomeration spots (gloss unevenness) of yellowinks is smaller than that of black inks. Therefore, a content ofcomponent (B) of 10 mass % or more is sufficient. If the content ofcomponent (B) is out of the above-mentioned range, tendencies similar tothose in the black inks are caused.

1.1.3. N-Vinyl Caprolactam (C)

The radiation-curable ink composition according to the embodiment mayfurther contain N-vinyl caprolactam (C) as a reaction component. In theradiation-curable ink composition according to the embodiment containingN-vinyl caprolactam (C) as the reaction component, the adhesion betweena recording medium and an image recorded thereon can be enhanced. Inaddition, N-vinyl caprolactam (C) has a good curing property and showsgood reducibility for other acrylate monomers and does not inhibitfunctions of other acrylate monomers.

When the total mass of the reaction components is assumed to be 100 mass%, the content of N-vinyl caprolactam (C) is preferably from 5 to 20mass % and more preferably 10 to 15 mass %. If the content of N-vinylcaprolactam (C) in the total reaction components is lower than 5 mass %,the adhesion between a recording medium and an image recorded thereonmay not be enhanced. On the other hand, if the content is higher than 20mass %, since the storage stability of the radiation-curable inkcomposition may not be good, the ink composition may not be suitable tobe used as a product.

1.1.4. Aminoacrylate (D)

The radiation-curable ink composition according to the embodiment mayfurther contain an aminoacrylate (D) as a reaction component. In theradiation-curable ink composition according to the embodiment containingaminoacrylate (D) as the reaction component, the copolymerizationreaction of a film discharged on a recording medium can be accelerated.As an example of specific functional effects, the amount of energynecessary for curing a film by irradiation of active radiation having amaximum emission wavelength ranging from 350 to 400 nm can be reduced bythat the ink composition contains a predetermined amount ofaminoacrylate (D) in the total reaction components and a polymerizationinitiator described below. By doing so, the film can be cured rapidly,even if active radiation is irradiated using a light source emitting lowenergy, such as an LED. Note that the term “curing” in the inventionrefers to a state that no stickiness is felt when a recorded matter istouched with a finger, that is, refers to a so-called tack-free state.

Examples of commercially available aminoacrylate (D) include EBECRYL7100 (a product of Daicel-Cytec Company Ltd.) and CN371 (a product ofSartomer Company).

When the total mass of the reaction components is assumed to be 100 mass%, the content of aminoacrylate (D) is preferably from 1 to 5 mass %. Ifthe content of aminoacrylate (D) in the total reaction components islower than 1 mass %, the copolymerization reaction does not smoothlyprogress, and the curing property of an image recorded on a recordingmedium may be insufficient. However, a content of higher than 5 mass %,does not improve the effect of accelerating the copolymerizationreaction and is therefore an excessive amount, which is not preferred.In addition, the viscosity of the ink composition is increased, whichmay deteriorate ink-discharging stability in an ink jet recordingapparatus and may cause yellowing of an image recorded on a recordingmedium.

1.1.5. Monofunctional Acrylate (2) Having an Alicyclic Structure

The radiation-curable ink composition according to the embodiment mayfurther contain a monofunctional acrylate (E) having an alicyclicstructure as a reaction component. In the radiation-curable inkcomposition according to the embodiment containing the monofunctionalacrylate (E) having an alicyclic structure as the reaction component,since the viscosity of the monofunctional acrylate is generally low, theradiation-curable ink composition can have a low viscosity (from 10 to40 mPa·s at 20° C.) suitable for an ink jet recording system.Furthermore, the bulky alicyclic structure can provide toughness to animage recorded on a recording medium, improving the scratch resistanceof the image.

Examples of monofunctional acrylate (E) having an alicyclic structureinclude dicyclopentenyloxyethyl acrylate, dicyclopentenyl acrylate,dicyclopentanyl acrylate, isobornyl acrylate, trimethylolpropane formalmonoacrylate, adamantyl acrylate, oxetane acrylate, and3,3,5-trimethylcyclohexane acrylate. These monofunctional acrylatemonomers may be used alone or in combination of two or more.

When the total mass of the reaction components is assumed to be 100 mass%, the content of monofunctional acrylate (E) having an alicyclicstructure is preferably from 5 to 50 mass %. If the content ofmonofunctional acrylate (E) having an alicyclic structure in the totalreaction components is lower than 5 mass %, the viscosity of the inkcomposition is increased, which may deteriorate the ink-dischargingstability in an ink jet recording apparatus. On the other hand, if thecontent is higher than 50 mass % so that the content of component (A) isrelatively reduced, the flexibility of an image recorded on a recordingmedium tends to be reduced to readily cause cracking in the imagerecorded on the recording medium. When the content of component (B) isrelatively decreased, agglomeration spots (gloss unevenness) may occuron the surface of an image recorded on a recording medium.

1.2. Black Pigment (F1)/Yellow Pigment (F2)

The radiation-curable ink composition according to the embodimentcontains either a black pigment or a yellow pigment, in addition to theabove-described reaction components.

A black pigment that can be used in the embodiment is, for example,carbon black. Examples of the carbon black include C.I. pigment black 7,specifically, products of Mitsubishi Chemical Corporation, such as No.2300, No. 900, MCF88, No. 33, No. 40, No. 45, No. 52, MA7, MA8, MA100,and No. 2200B; products of Columbia Chemical Company, such as Raven5750, Raven 5250, Raven 5000, Raven 3500, Raven 1255, and Raven 700;products of Cabot Corporation, such as Regal 400R, Regal 330R, Regal660R, Mogul L, Mogul 700, Monarch 800, Monarch 880, Monarch 900, Monarch1000, Monarch 1100, Monarch 1300, and Monarch 1400; products of DegussaCo., such as Color Black FW1, Color Black FW2, Color Black FW2V, ColorBlack: FW18, Color Black FW200, Color Black S150, Color Black S160,Color Black S170, Printex 35, Printer U, Printex V, Printex 140U,Special Black 6, Special Black 5, Special Black 4A, and Special Black 4;and products of Ciba Japan K.K., such as Microlith Black C-K.

Example of the yellow pigment that can be used in the embodiment includeC.I. pigment yellow 1, 2, 3, 12, 13, 14, 16, 17, 73, 74, 75, 83, 93, 95,97, 98, 109, 110, 114, 120, 128, 129, 138, 150, 151, 154, 155, 180, 185,and 213.

The pigment that can be used in the embodiment preferably has an averageparticle diameter ranging from 10 to 200 nm, more preferably from 50 to150 nm.

The amount of a pigment contained in the radiation-curable inkcomposition according to the embodiment is preferably from 0.1 to 25parts by mass and more preferably 0.5 to 15 parts by mass based on 100parts by mass of the total reaction components.

The radiation-curable ink composition according to the embodiment maycontain a dispersant in order to increase the dispersing property of thepigment. Examples of the dispersant that can be used in the embodimentinclude high-molecular dispersants such as Solsperse 3000, Solsperse5000, Solsperse 9000, Solsperse 12000, Solsperse 13240, Solsperse 17000,Solsperse 24000, Solsperse 26000, Solsperse 28000, and Solsperse 36000,which are available from Lubrizol Corporation; and Discole N-503,Discole N-506, Discole N-509, Discole N-512, Discole N-515, DiscoleN-518, and Discole N-520, which are available from Dai-ichi KogyoSeiyaku Co., Ltd.

1.3. Photopolymerization Initiator

The radiation-curable ink composition according to the embodiment mayfurther contain a photopolymerization initiator, in addition to theabove-described reaction components. The photopolymerization initiatoris a collective term of compounds having a function of initiatingcopolymerization reaction of the above-mentioned reaction components byirradiating the radiation-curable ink composition discharged on arecording medium with active radiation.

Examples of the photopolymerization initiator include knownphotopolymerization initiators such as alkylphenone-basedphotopolymerization initiators, acyl phosphine oxide-basedphotopolymerization initiators, titanocene-based photopolymerizationinitiators, and thioxanthone-based photopolymerization initiators. Amongthem, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, which isexcellent in compatibility with the above-mentioned reaction components,molecule-cleaving type initiators such asbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, which has a broadlight absorbing spectrum, and hydrogen abstraction-type initiators suchas diethyl thioxantone are preferred. In the acyl phosphine oxide-basedphotopolymerization initiators, since the chromophore structure afterits photocleavage is highly different from that before thephotocleavage, the absorption spectrum largely changes to cause adecrease in absorption, so-called photobleaching. Accordingly, the acylphosphine oxide-based photopolymerization initiators are preferred. Inaddition, though the absorption of the acyl phosphine oxide-basedphotopolymerization initiators ranges from the UV region to the VLregion, the initiators hardly cause yellowing and are also excellent ininternal curing. Therefore, the initiators are particularly preferredfor transparent films having large thicknesses and films containingpigments having high hiding power. In the thioxantone-basedphotopolymerization initiators, the initiators react with oxygenremaining in the reaction system after the photocleavage to reduce theconcentration of oxygen in the system. Since the degree of inhibition ofradical polymerization can be reduced by the amount of decrease inconcentration of oxygen, the curing property of the surface can beimproved. Accordingly, the thioxantone-based photopolymerizationinitiators are preferred. Furthermore, a combination of an acylphosphine-based photopolymerization initiator and a thioxanthone-basedphotopolymerization initiator is particularly preferred. Thesephotopolymerization initiators may be used alone, but the use incombination of two or more can maximize the respective characteristics.

When the total mass of the reaction components is assumed to be 100 mass%, the content of the photopolymerization initiator is preferably from 1to 20 parts by mass and more preferably from 5 to 15 parts by mass. Whenthe content is less than 1 part by mass based on 100 parts by mass ofthe total reaction components, the function of the photopolymerizationinitiator may not be exhibited, and the curing property of an imagerecorded on a recording medium may be insufficient. However, a contentof higher than 20 parts by mass does not improve the effect ofinitiating the copolymerization reaction and is therefore an excessiveamount, which is not preferred.

1.4. Other Additives

The radiation-curable ink composition according to the embodiment maycontain a reaction component other than the above-mentioned reactioncomponents and an additive such as a slip agent or a polymerizationinhibitor, according to need.

It is preferable that the radiation-curable ink composition according tothe embodiment do not contain organic solvents and be a solventlessradiation-curable ink composition.

The reaction component other than the above-mentioned reactioncomponents is preferably an acrylate monomer having a glass transitiontemperature of 0° C. or less as shown below, which does not deterioratethe flexibility of an image recorded on a recording medium.

Long-Chain Alkyl Acrylate

Examples of the long-chain alkyl acrylate include 2-ethylhexyl acrylate,n-octyl acrylate, n-nonyl acrylate, n-decyl acrylate, isooctyl acrylate,n-lauryl acrylate, n-tridecyl acrylate, n-cetyl acrylate, n-stearylacrylate, isomyristyl acrylate, and isostearyl acrylate.

Polyethylene Oxide or Polypropylene Oxide Adduct Monofunctional Acrylate

Examples of the polyethylene oxide or polypropylene oxide adductmonofunctional acrylate include (poly)ethylene glycol monoacrylate,(poly)ethylene glycol acrylate methyl ester, (poly)ethylene glycolacrylate ethyl ester, (poly)ethylene glycol acrylate phenyl ester,(poly)propylene glycol monoacrylate, (poly)propylene glycol monoacrylatephenyl ester, (poly)propylene glycol acrylate methyl ester,(poly)propylene glycol acrylate ethyl ester, methoxytriethylene glycolacrylate, methoxydipropylene glycol acrylate, ethoxydiethylene glycolacrylate, and methoxy-polyethylene glycol acrylate.

Phenoxyethyl Acrylate Modification

Examples of the phenoxyethyl acrylate modification includephenoxydiethylene glycol acrylate, phenoxy-polyethylene glycol acrylate,2-hydroxy-3-phenoxypropyl acrylate, and nonylphenol EO adduct acrylate.

The radiation-curable ink composition according to the embodiment maycontain a slip agent. The slip agent that can be used in the embodimentis preferably a silicone-based surfactant and more preferably polyestermodified silicone or polyether modified silicone. Specifically, examplesof the polyester modified silicone include BYK-347, BYK-348, BYK-UV3500, BYK-UV 3510, and BYK-UV 3530 (which are products of BYK-ChemieJapan K.K.), and examples of the polyether modified silicone includeBYK-3570 (which is a product of BYK-Chemie Japan K.K.).

The radiation-curable ink composition according to the embodiment maycontain a polymerization inhibitor. Examples the polymerizationinhibitor that can be used in the embodiment include hydroquinone,benzoquinone, and p-methoxyphenol.

1.5. Physical Properties

The radiation-curable ink composition according to the embodimentpreferably has a viscosity of from 10 to 40 mPa·s at 20° C. and morepreferably from 15 to 25 mPa·s. When the radiation-curable inkcomposition has a viscosity in this range at 20° C., a nozzle candischarge a suitable amount of the radiation-curable ink composition,and curved flight or scattering of the radiation-curable ink compositioncan be further decreased. Therefore, the ink composition can be suitablyused in an ink jet recording apparatus. The viscosity can be measuredusing a viscoelasticity meter MCR-300 (a product of Physica) at anenvironment of 20° C. by reading the viscosity at a shear rate of 200,while the shear rate being increased from 10 to 1000.

The radiation-curable ink composition according to the embodimentpreferably has a surface tension of from 20 to 30 mN/m at 20° C. Whenthe radiation-curable ink composition has a surface tension in thisrange at 20° C., the radiation-curable ink composition hardly makes aliquid-repellent nozzle wet. With this, the nozzle can discharge asuitable amount of the radiation-curable ink composition, and curvedflight or scattering of the radiation-curable ink composition can befurther decreased. Therefore, the ink composition can be suitably usedin an ink jet recording apparatus. The surface tension can be measuredusing an auto surface tensiometer CBVP-Z (a product of Kyowa InterfaceScience Co., Ltd.) at an environment of 20° C. by determining thesurface tension when a platinum plate is wetted with the ink.

2. INK JET RECORDING METHOD

An ink jet recording method according to an embodiment, of the inventionincludes the steps of (a) discharging the above-describedradiation-curable ink composition on a recording medium and (b)irradiating the discharged radiation-curable ink composition with activeradiation having a peak emission wavelength ranging from 350 to 400 nmusing an active radiation source.

Each step of the ink jet recording method according to the embodimentwill be described below.

2.1. Step (a)

This step is a step of discharging the above-described radiation-curableink composition on a recording medium.

Since the radiation-curable ink composition has been described, detaileddescription thereof is omitted.

The recording medium is not particularly limited, and examples thereofinclude plastics such as polyvinyl chloride, polyethylene terephthalate,polypropylene, polyethylene, and polycarbonate; these plastics havingprocessed surfaces; glass; and coated paper.

The radiation-curable ink composition can be discharged by, for example,using an ink jet recording apparatus described below.

FIG. 1 is a perspective view of an ink jet recording apparatus that canbe used in the ink jet recording method according to the embodiment.

The ink jet recording apparatus 20 shown in FIG. 1 includes a motor 30for transporting a recording medium P in a sub-scanning direction SS, aplaten 40, a printing head 52 serving as a recording head that spraysmicroparticles of the radiation-curable ink composition from a headnozzle to discharge them onto the recording medium P, a carriage 50 onwhich the printing head 52 is mounted, a carriage motor 60 for movingthe carriage 50 in a main-scanning direction MS, and a pair of activeradiation-irradiating devices 90A and 90B for irradiating with activeradiation the ink-adhering surface of the recording medium P on whichthe radiation-curable ink composition has been discharged by theprinting head 52.

The carriage 50 is towed by a tow belt 62 driven by the carriage motor60 and moves along a guide rail 64.

The printing head 52 shown in FIG. 1 is a serial head that sprays threeor more colors of inks for full-color printing and is provided with alarge number of head nozzles for each color. The printing head 52 ismounted on the carriage 50 on which a black cartridge 54 being a blackink container containing a black ink which is supplied to the printinghead 52 and a color ink cartridge 56 being a color ink containercontaining color inks which are supplied to the printing head 52 aremounted, in addition to the printing head 52. The ink contained in eachof the cartridges 54 and 56 is the radiation-curable ink compositiondescribed above.

The ink jet recording apparatus 20 is provided with a capping device 80for sealing the nozzle face of the printing head 52 during the stoppageat the home position (the position on the right side of FIG. 1) of thecarriage 50. When the carriage 50 after completion of a printing jobreaches above the capping device 80, the capping device 80 isautomatically lifted by a mechanism (not shown) to seal the nozzle faceof the printing head 52. By the capping, inks in the nozzles areprevented from drying. The control of positioning the carriage 50 isperformed for, for example, precisely positioning the carriage 50 at theposition of the capping device 80.

The radiation-curable ink composition can be discharged on a recordingmedium by using such an ink jet recording apparatus 20. By using the inkjet recording apparatus 20, the steps (a) and (b) can be sequentiallyperformed by a single apparatus, without using separate apparatuses forrespectively performing the steps (a) and (b).

2.2 Step (b)

This step is a step for irradiating the discharged radiation-curable inkcomposition with active radiation having a peak emission wavelengthranging from 350 to 400 nm using an active radiation source. Accordingto this step, the radiation-curable ink composition discharged on therecording medium is cured by being irradiated with active radiationhaving a specific wavelength to record an image on the recording medium.

A case where the step (b) is performed using the above-described ink jetrecording apparatus 20 will be described in detail below.

FIG. 2 is a front view of the active radiation-irradiating devices 90A(corresponding to 190A in FIG. 2) and 90B (corresponding to 190B in FIG.2) shown in FIG. 1. FIG. 3 is a fragmentary view taken in the directionof the arrows III-III of FIG. 2.

As shown in FIGS. 1 to 3, the active radiation-irradiating devices 190Aand 190B are respectively attached to the both ends along the movingdirection of the carriage 50.

As shown in FIG. 2, the active radiation-irradiating device 190Aattached on the left side of the printing head 52 performs activeradiation irradiation against an ink layer 196 discharged on therecording medium P in rightward scanning in which the carriage 50 movestoward the right direction (the direction shown by the arrow B in FIG.2). On the other hand, the active radiation-irradiating device 190Battached on the right side of the printing head 52 performs activeradiation irradiation against the ink layer 196 discharged on therecording medium P in leftward scanning in which the carriage 50 movestoward the left direction (the direction shown by the arrow C in FIG.2).

The active radiation-irradiating devices 190A and 190B each include acase 194 attached to the carriage 50 and align-supporting an activeradiation source 192 and a light source-controlling circuit (not shown)for controlling on/off of emission by the active radiation source 192.As shown in FIGS. 2 and 3, each of the active radiation-irradiatingdevices 190A and 190B is provided with one active radiation source 192,but may be provided with two or more active radiation sources 192. Theactive radiation source 192 is preferably an LED or LD. By doing so,since equipment such as a filter is unnecessary, the active radiationsource can be prevented from being increased in size, compared to a casewhere a mercury lamp, a metal halide lamp, or another lamp is used asthe active radiation source. In addition, since the emitted activeradiation is not absorbed by a filter, the intensity of the activeradiation is not reduced, and therefore, the radiation-curable incomposition can be efficiently cured.

The wavelengths of the radiation emitted by the active radiation sources192 may be the same or different from each other. When the activeradiation source 192 is an LED or LD, the peak emission wavelength ofemitted active radiation may be in the range of about 350 to 400 nm.

According to the active radiation-irradiating devices 190A and 190Bdescribed above, as shown in FIG. 2, the ink layer 196 adhering on therecording medium P by being discharged from the printing head 52 isirradiated with active radiation 192 a from the active radiation source192 that irradiates on the recording medium P in the area near theprinting head 52. As a result, the surface and the inside of the inklayer 196 can be cured.

Since the irradiation dose of the active radiation varies depending onthe thickness of the ink layer 196 adhering on the recording medium Pand cannot be therefore strictly specified, proper conditions aredetermined in each case. However, since the radiation-curable inkcomposition described above is used, the ink layer 196 can besufficiently cured with an irradiation dose of from 300 to 1000 mJ/cm².

According to the ink jet recording apparatus 20, even in full-colorprinting of a relatively thin ink layer with the radiation-curable inkcomposition having a low viscosity, a plurality of radiation-curable inkcompositions discharged on the recording medium P can be satisfactorilycured without causing problems such as bleeding and color mixing.

The structure of the ink jet recording apparatus 20 is not limited tothat including the recording head, carriage, and active radiation sourcedescribed above and can employ various configurations based on thepurpose of the ink jet recording method according to the embodiment.

3. RECORDED MATTER

The recorded matter according to an embodiment of the invention is thatrecorded by the above-described ink jet recording method. Since an imagerecorded on a recording medium is that formed using the above-describedradiation-curable ink composition, the image is excellent in flexibilityand can be inhibited from causing agglomeration spots (gloss unevenness)on the surface thereof.

Purpose of the recorded matter according to the embodiment is notparticularly limited, and the recorded matter can be used as an imagerecorded on the above-mentioned recording medium. Since the imagerecorded on the recording medium is excellent in flexibility, therecorded matter is particularly suitable for the purpose of being stuckon an article that is required to have a bending or stretchingcapability.

4. EXAMPLES

The invention will be more specifically described by Examples below, butis not limited to these Examples.

4.1. Preparation of Pigment Dispersion 4.1.1. Preparation of BlackPigment Dispersion

A mixture was prepared by adding phenoxyethyl acrylate (a product ofOsaka Organic Chemical Industry Ltd., trade name “V#192”) to 15 parts bymass of a black pigment (a product of Ciba Japan K.K., trade name“Microlith Black C-K”) being a colorant and 3 parts by mass of Solsperse36000 (a product of Lubrizol Corporation) being a dispersant to make thetotal amount 100 parts by mass and mixing and stirring them. Thismixture was subjected to dispersing treatment with zirconia beads(diameter: 1.5 mm) for 6 hours using a sand mill (a product of YasukawaSeisakusyo Co., Ltd.). Then, the zirconia beads were separated with aseparator to obtain a black pigment dispersion to be used in Examplesand Comparative Examples.

4.1.2 Preparation of Yellow Pigment Dispersion

A mixture was prepared by adding phenoxyethyl acrylate (a product ofOsaka Organic Chemical Industry Ltd., trade name “V#192”) to 12 parts bymass of a yellow pigment (a product of Ciba Japan K.K., trade name“Cromophtal Yellow LA”) being colorant and 2.4 parts by mass ofSolsperse 36000 (a product of Lubrizol Corporation) being a dispersantto make the total amount 100 parts by mass and mixing and stirring them.This mixture was subjected to dispersing treatment with zirconia beads(diameter: 1.5 mm) for 6 hours using a sand mill (a product of YasukawaSeisakusyo Co., Ltd.). Then, the zirconia beads were separated with aseparator to obtain a yellow pigment dispersion to be used in Examplesand Comparative Examples.

4.2. Preparation of Radiation-Curable Ink Composition

Reaction components, photopolymerization initiators, a slip agent, and apolymerization inhibitor were mixed to completely dissolve for obtainingcomposites shown in Tables 1 and 2, and the black pigment dispersion orthe yellow pigment dispersion was dropped to each composite withstirring to give a pigment concentration shown in Table 1 or 2. Aftercompletion of the dropping, the mixture was red at ordinary temperaturefor 1 hour and was subsequently subjected to filtration through amembrane filter of 5 μm pore size to obtain each radiation-curable inkcomposition.

The components shown in Tables 1 and 2 are as follows:

Phenoxyethyl acrylate (a product of Osaka Organic Chemical IndustryLtd., trade name “V#192”)

Tetraethylene glycol diacrylate (a product of Osaka Organic ChemicalIndustry Ltd., trade name “V#335HP”)

Tripropylene glycol diacrylate (a product of Shin-Nakamura Chemical Co.,Ltd. trade name “APG-200”)

Dipropylene glycol diacrylate (a product of Shin-Nakamura Chemical Co.,Ltd. trade name “APG-100”)

N-Vinyl caprolactam (a product of BASF SE, trade name “N-VinylCaprolactam”)

Aminoacrylate (a product of Daicel-Cytec Company Ltd., trade name“EBECRYL 7100”)

Dicyclopentenyloxyethyl acrylate (Hitachi Chemical Company, Ltd., tradename “FA512AS”)

Isobornyl acrylate (a product of Osaka Organic Chemical Industry Ltd.,trade name “IBXA”)

IRGACURE 819 (a product of Ciba Japanbis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, photopolymerizationinitiator)

DAROCUR TPO (a product of Ciba Japan K.K.,(2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, photopolymerizationinitiator)

DETX (a product of Nippon Kayaku Co., Ltd., photosensitizer)

BYK-UV 3500 (a product of BYK-Chemie Japan K.K., polydimethylsiloxanehaving a polyether modified acryl group, slip agent)

p-Methoxyphenol (a product of Kanto Chemical Co., Ltd., polymerizationinhibitor)

Carbon black (a product of Ciba Japan K.K., black pigment)

Pigment yellow 180 (a product of Ciba Japan K.K., yellow pigment)

Solsperse 36000 (a product of LUBRIZOL Corporation, dispersant)

4.3. Producing of Recorded Matter

Nozzles in columns were filled with respective radiation-curable inkcompositions using an ink jet printer PX-G5000 (a product of Seiko EpsonCorporation). Solid pattern images were printed on PVC films (a productof 3M, trade name “IJ180-10”) at ordinary temperature and ordinarypressure by ink dots having a middle-sized diameter so that thethickness of each printed matter was 10 μm. The solid pattern imageswere cured by being subjected to first irradiation with UV light havinga wavelength of 385 nm at an irradiation intensity of 100 mW/cm² andthen second irradiation with UV light having a wavelength of 395 nm atan irradiation intensity of 1000 mW/cm² so that the accumulated lightquantity was 700 mJ/cm² with UV-LEDs in UV-irradiating devices mountedon the sides of the carriage. Thus, recorded matters where the solidpattern images were printed on PVC films were prepared.

4.4. Evaluation Test

The resulting recorded matters were evaluated by the following tests.The evaluation tests were all performed at room temperature.

4.4.1. Evaluation of Agglomeration Spots (Gloss Unevenness)

The resulting recorded matters were visually evaluated for the presenceor absence of agglomeration spots (gloss unevenness). The evaluationcriteria are as follows:

A: no agglomeration spots occurred on the surface of a recorded matter,and gloss was recognized on the surface;

B: agglomeration spots slightly occurred on the surface of a recordedmatter, and gloss unevenness was observed on the surface; and

C: distinct agglomeration spots occurred on the surface of a recordedmatter, and gloss unevenness was recognized on the surface.

Note that criteria “A” is most desirable in the evaluation ofagglomeration spots (gloss unevenness).

4.4.2. Evaluation of Flexibility

Each recorded matter was cut into a predetermined size (the length atthis stage was defined as L₀) and set to a tensile tester (a product ofA&D Co., Ltd.). The recorded matter was stretched at a tensile rate of100 mm/min with the tensile tester, and the moment that cracking orpeeling (hereinafter, referred to as “cracking, etc.”) occurred in therecorded matter was visually confirmed. The length of the stretchedrecorded matter was calculated based on the time from the starting ofthe stretching till occurrence of cracking, etc. and was defined as L₁.The flexibility of the recorded matter was evaluated by calculating thedegree (%) of elongation at occurrence of cracking, etc. in the imageformed on the PVC film from the following expression:

Degree (%) of elongation at occurrence of cracking, etc. in image=[(L ₁−L ₀)/L ₀]×100   (1)

The evaluation criteria are as follows:

AAA: the degree of elongation is 180% or more;

AA: the degree of elongation is 160% or more but less than 180%;

A: the degree of elongation is 140% or more but less than 160%;

B: the degree of elongation is 120% or more but less than 140%;

C: the degree of elongation is 100% or more but less than 120%; and

D: the degree of elongation is less than 100%.

4.4.3. Evaluation of Adhesion

The adhesion between the PVC film and the image was evaluated inaccordance with JIS K 5600-5-6 (Testing methods for paints—Part 5:Mechanical property of film—Section 6: Adhesion test (Cross-cut test)).The evaluation criteria are as follows:

0: edges of cuts completely smooth, and no peeling occurs in all gridsections;

1: small peeling of film is recognized at intersections of cuts;

2: film is peeled along edges and/or at intersections of cuts;

3: film is partially or entirely peeled along edges of cuts and/orpartially or entirely peeled at various portions of grid sections;

4: film is partially or entirely peeled along edges of cuts and/orpartially or entirely peeled at several grid sections; and

5: the degree of peeling is higher than criteria 4.

4.5. Evaluation Results

The results of the evaluation tests are also shown in Tables 1 and 2.Table 1 shows the results of the radiation-curable black inkcompositions, and Table 2 shows the results of the radiation-curableyellow ink compositions.

TABLE 1 Com- Com- Com- Exam- parative parative parative Component ple 1Example 2 Example 3 Example 4 Example 1 Example 2 Example 3 ReactionComponent (A) (mass %) Phenoxyethyl acrylate 52.0 26.7 30.7 20.0 65.618.5 component Component (B) (mass %) Tetraethylene glycol 7.0 5.1 25.0diacrylate Tripropylene glycol 25.0 23.0 25.0 25.0 diacrylateDipropylene glycol 23.5 25.0 23.0 25.1 9.4 12.5 49.4 diacrylateComponent (C) (mass %) N-Vinyl caprolactam 14.0 18.9 13.3 5.6 10.0 21.2Component (D) (mass %) Aminoacrylate 3.7 4.4 4.0 7.0 3.5 4.5 4.4Component (E) (mass %) Dicyclopentenyloxyethyl 6.0 16.4 4.5 acrylateIsobornyl acrylate 6.8 35.3 Total amount 100.0 100.0 100.0 100.0 100.0100.0 100.0 Additive Photopolymerization IRGACURE 819 6.0 6.0 6.0 6.06.0 6.0 6.0 initiator (parts by mass) DAROCUR TPO 5.0 5.0 5.0 5.0 5.05.0 5.0 DETX 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Slip agent (part by mass)BYK-UV 3500 0.2 0.2 0.2 0.2 0.2 0.2 0.2 Polymerization inhibitorp-Methoxyphenol 0.2 0.2 0.2 0.2 0.2 0.2 0.2 (parts by mass) Pigment(parts by mass) Carbon black 2.5 2.5 2.5 2.5 2.5 2.5 2.5 Dispersant(parts by mass) Solsperse 36000 0.5 0.5 0.5 0.5 0.5 0.5 0.5 EvaluationAgglomeration spot (gloss PVC film A A A A C A A result unevenness)Cracking etc. PVC film AA C B A AAA D D Degree of elongation (%)Adhesion PVC film 0 0 0 0 5 0 0

TABLE 2 Com- Com- Com- parative parative parative Component Example 5Example 6 Example 7 Example 4 Example 5 Example 6 Reaction Component (A)(mass %) Phenoxyethyl acrylate 45.0 53.0 25.6 58.9 53.3 15.6 componentComponent (B) (mass %) Tetraethylene glycol diacrylate 15.0 12.0Tripropylene glycol diacrylate 6.0 12.0 4.0 30.0 Dipropylene glycoldiacrylate 15.0 7.0 25.0 4.0 30.0 Component (C) (mass %) N-Vinylcaprolactam 15.0 20.0 15.4 13.7 14.2 13.6 Component (D) (mass %)Aminoacrylate 4.5 4.5 4.5 4.5 4.5 4.5 Component (E) (mass %)Dicyclopentenyloxyethyl 5.5 9.5 5.5 22.9 20.0 6.3 acrylate Total amount100.0 100.0 100.0 100.0 100.0 100.0 Additive Photopolymerizationinitiator IRGACURE 819 6.0 5.5 5.0 5.5 5.5 5.0 (parts by mass) DAROCURTPO 5.0 4.5 4.5 4.5 4.5 4.5 DETX 3.0 1.5 1.5 1.5 1.5 1.5 Slip agent(part by mass) BYK-UV 3500 0.2 0.2 0.2 0.2 0.2 0.2 Polymerizationinhibitor (parts p-Methoxyphenol 0.2 0.2 0.2 0.2 0.2 0.2 by mass)Pigment (parts by mass) Pigment yellow 180 3.0 3.0 3.0 3.0 3.0 3.0Dispersant (parts by mass) Solsperse 36000 0.6 0.6 0.6 0.6 0.6 0.6Evaluation Agglomeration spot (gloss PVC film A A A B B A resultunevenness) Cracking etc. PVC film A AA C AAA AA D Degree of elongation(%) Adhesion PVC film 0 0 0 0 0 0

In the radiation-curable black ink compositions of Examples 1 to 4 shownin Table 1 and the radiation-curable yellow ink compositions of Examples5 to 7 shown in Table 2, no agglomeration spots occurred on the surfaceof every recorded matter, and gloss was confirmed on the surface. Inaddition, since the degree of elongation at occurrence of cracking, etc.was 100% or more, the results showed that every recorded matter wasexcellent in flexibility and also that the adhesion was satisfactory.

On the other hand, in the radiation-curable black ink composition ofComparative Example 1 shown in Table 1 containing component (A) in anamount of larger than 55 mass % and component (B) in an amount smallerthan 20 mass % of the total reaction components, distinct agglomerationspots occurred on the surface of the recorded matter, and glossunevenness was recognized on the surface. In addition, since the inkcomposition did not contain component (C), the result showed that theadhesion between the recording medium and the recorded matter recordedthereon was insufficient.

In the radiation-curable black ink composition of Comparative Example 2shown in Table 1 containing component (A) in an amount of smaller than20 mass % and component (B) in an amount larger than 50 mass % of thetotal reaction components, the degree of elongation at occurrence ofcracking, etc. was less than 100%, and the result showed that theflexibility of the recorded matter was insufficient.

In the radiation-curable black ink composition of Comparative Example 3shown in Table 1 containing component (B) in an amount larger than 50mass % of the total reaction components and not containing component(A), the degree of elongation at occurrence of cracking, etc. was lessthan 100%, and the result showed that the flexibility of the recordedmatter was insufficient.

In the radiation-curable yellow ink composition of Comparative Example 4shown in Table 2 not containing component (B) in the reactioncomponents, agglomeration spots occurred slightly on the surface of therecorded matter, and gloss unevenness was recognized on the surface.However, since the content of component (A) was larger than 55 mass %,the flexibility of the recorded matter was notably excellent.

In the radiation-curable yellow ink composition of Comparative Example 5shown in Table 2 containing component (B) in an amount smaller than 10mass % of the total reaction components, agglomeration spots occurredslightly on the surface of the recorded matter, and gloss unevenness wasobserved on the surface. However, the ink composition containedcomponent (A) in an amount of 53.3 mass %, the recorded matter wasexcellent in flexibility of the recorded matter.

In the radiation-curable yellow ink composition of Comparative Example 6shown in Table 2 containing component (B) in an amount larger than 50mass % of the total reaction components, no agglomeration spots occurredon the surface of the recorded matter, and the gloss was recognized onthe surface. However, since the content of component (A) was smallerthan 20 mass %, the degree of elongation at occurrence of cracking, etc.was smaller than 100%, and the result showed the flexibility of therecorded matter was insufficient.

The invention is not limited to the above-described embodiments, andvarious modifications are possible. For example, the invention includessubstantially the same structures as those described in the embodiments(for example, a structure in which the function, the method, and theresults are the same or a structure in which the purpose and the effectare the same). The invention includes structures in which portions thatare not essential in the structures described in the embodiments aresubstituted. The invention includes structures that perform the samefunctions and effects or structures that can achieve the same purpose asthose described in the embodiments. The invention includes structures inwhich known technologies are added to the structures described in theembodiments.

What is claimed is:
 1. A radiation-curable ink composition comprising: phenoxyethyl acrylate (A) in an amount of from 20 to 55 mass % of the total reaction components; a multifunctional acrylate (B) in an amount of from 20 to 50 mass % of the total reaction components; N-vinyl caprolactam (C) in an amount of 20 mass % or less of the total reaction components; and a black pigment (F1).
 2. The radiation-curable ink composition according to claim 1, wherein the amount of N-vinyl caprolactam is in the range of 5 to 20 mass %.
 3. A radiation-curable ink composition comprising: phenoxyethyl acrylate (A) in an amount of from 20 to 55 mass % of the total reaction components; a multifunctional acrylate (B) in an amount of from 10 to 50 mass % of the total reaction components; N-vinyl caprolactam (C) in an amount of 20 mass % or less of the total reaction components; and a yellow pigment (F2).
 4. The radiation-curable ink composition according to claim 3, wherein the amount of N-vinyl caprolactam is in the range of 5 to 20 mass %. 